Table of Contents
- xBIOS Overview
- General Notes
- Download Location
- Autorun
- Filename Format
- xBIOS Limitations
- Default Memory Layout
- Disk Images
- Practical Usage
- Examples
- xBIOS_RENAME_ENTRY
- xBIOS_LOAD_FILE
- xBIOS_OPEN_FILE
- xBIOS_LOAD_DATA
- xBIOS_WRITE_DATA
- xBIOS_OPEN_CURRENT_DIR
- xBIOS_GET_BYTE
- xBIOS_PUT_BYTE
- xBIOS_FLUSH_BUFFER
- xBIOS_SET_LENGTH
- xBIOS_SET_INIAD
- xBIOS_SET_FILE_OFFSET
- xBIOS_SET_RUNAD
- xBIOS_SET_DEFAULT_DEVICE
- xBIOS_OPEN_DIR
- xBIOS_LOAD_BINARY_FILE
- xBIOS_OPEN_DEFAULT_DIR
- xBIOS_SET_DEVICE
- xBIOS_RELOCATE_BUFFER
- xBIOS_GET_ENTRY
- xBIOS_OPEN_DEFAULT_FILE
- xBIOS_READ_SECTOR
- xBIOS_FIND_ENTRY
- xBIOS_SET_BUFFER_SIZE
- Counters During I/O
- Playing Music During I/O
- Indexed Data within File - LZ4 Graphics Decompression
- Use of High Speed Devices
- Detecting High Speed Devices
- Using Alternative Disk Drives
- Checking if Alternative Disk Drives Exist
- Varying Directory Sizes
- xBOOT
xBIOS Overview#
xBIOS is like a programmers version of DOS. With it you can easily access files from your programs without using Atari DOS. It is smaller than DOS and therefore saves memory in your programs. You can even run programs from as low as $0200, however $0800 or $2000 are more common.
General Notes#
In this section you will find some general notes about xBIOS and how it functions.
Download Location#
http://xxl.atari.pl
Autorun#
To allow an executable to auto run on bootup, have it named as “XAUTORUN”. If no such file exists on the disk, the xBIOS loader menu will appear.Filename Format#
The filenames are in 8.3 format but without the dot. Filenames are padded out to 11 characters and are converted to uppercase. Therefore, “file.txt” will become:
‘FILE TXT’ (4 letters, 4 spaces and a 3 character extension)
xBIOS is case insensitive.
xBIOS Limitations#
a) New files cannot be created.
b) Existing files cannot be extended in length.
c) New directories cannot be created programatically.
Default Memory Layout#
$0000-$00FF Free $0200-$06FF Free $0700-$07FF xBIOS I/O buffer $0800-$0BFF xBIOS $0C00-$CFFF Free $D000-$D7FF Atari H/W $D800-$FFFF Free
Disk Images#
Disk images (.atr files) need to be prepared in advance for xBIOS to work.A disk image is a file which simulates a disk. It will contain 1 or more files which can be used by your programs.
In order to prepare them, an external tool needs to be used.
‘dir2atr’ : http://www.horus.com/~hias/atari
A tool for creating an ATR file from a folder.
‘franny’ : http://atariage.com/forums/topic/159325-program-to-add-to-and-extract-files-from-atr/
Allows the additional of individual files to an ATR file.
Practical Usage#
In order to have a disk which is usable, a project build system should complete the following steps:
a) Make a copy of the xBIOS.atr file, renaming the new file to something relevant for your project.
b) Add all the new files to the file. ‘franny’ and ‘dir2atr’ are good tools for this. Ensure that the program which you want to initially run is named ‘XAUTORUN’.
Example Windows batch file:
mads myProg.asm
copy /Y myProg.obx myatr\XAUTORUN
dir2atr -md -B xboot.obx myatr.atr myatr
pause
xBIOS now also needs adding into the development project which is being created.
There are two ways of achieving this:
Option 1: The following code needs to be pasted into a project:
(Valid for xBIOS v4.3)
xBIOS equ $800 xBIOS_VERSION equ xBIOS+$02 xBIOS_RENAME_ENTRY equ xBIOS+$03 xBIOS_LOAD_FILE equ xBIOS+$06 xBIOS_OPEN_FILE equ xBIOS+$09 xBIOS_LOAD_DATA equ xBIOS+$0c xBIOS_WRITE_DATA equ xBIOS+$0f xBIOS_OPEN_CURRENT_DIR equ xBIOS+$12 xBIOS_GET_BYTE equ xBIOS+$15 xBIOS_PUT_BYTE equ xBIOS+$18 xBIOS_FLUSH_BUFFER equ xBIOS+$1b xBIOS_SET_LENGTH equ xBIOS+$1e xBIOS_SET_INIAD equ xBIOS+$21 xBIOS_SET_FILE_OFFSET equ xBIOS+$24 xBIOS_SET_RUNAD equ xBIOS+$27 xBIOS_SET_DEFAULT_DEVICE equ xBIOS+$2a xBIOS_OPEN_DIR equ xBIOS+$2d xBIOS_LOAD_BINARY_FILE equ xBIOS+$30 xBIOS_OPEN_DEFAULT_DIR equ xBIOS+$33 xBIOS_SET_DEVICE equ xBIOS+$36 xBIOS_RELOCATE_BUFFER equ xBIOS+$39 xBIOS_GET_ENTRY equ xBIOS+$3c xBIOS_OPEN_DEFAULT_FILE equ xBIOS+$3f xBIOS_READ_SECTOR equ xBIOS+$42 xBIOS_FIND_ENTRY equ xBIOS+$45 xBIOS_SET_BUFFER_SIZE equ xBIOS+$48 xDIRSIZE equ xBIOS+$3e5 ; current directory size in sectors (1 byte) xSPEED equ xBIOS+$3e6 ; STANDARD SPEED (1 byte) xHSPEED equ xBIOS+$3e7 ; ULTRA SPEED (1 byte) xIRQEN equ xBIOS+$3e8 ; User IRQ (1 byte) xAUDCTL equ xBIOS+$3e9 ; AUDCTL xFILE equ xBIOS+$3ea ; File handle (2 bytes) xDIR equ xBIOS+$3ec ; Root directory handle (2 bytes) xIOV equ xBIOS+$3ee ; I/O module entry (2 bytes) xBUFFERH equ xBIOS+$3f0 ; Buffer adr hi byte (1 byte) xBUFSIZE equ xBIOS+$3f1 ; Buffer size lo byte $100-SIZE (1 byte) xDAUX3 equ xBIOS+$3f2 ; Buffer offset (1 byte) xSEGMENT equ xBIOS+$3f3 ; Bytes to go in binary file segment (2 bytes) xNOTE equ xBIOS+$3f5 ; File pointer (3 bytes) xDEVICE equ xBIOS+$3fc ; Device ID xDCMD equ xBIOS+$3fd ; CMD (1 byte) xDAUX1 equ xBIOS+$3fe ; Sector lo byte (1 byte) xDAUX2 equ xBIOS+$3ff ; Sector hi byte (1 byte)
Each entry in this jump table specifies where in memory that the code for each function resides. If you ever wish to start from a different address, change the value for ‘xBIOS’ above and change the value in the binary header of xBIOS.com.
Option 2: From xBIOS v4.2 and above, you can use the xBIOS.cfg file which is as below.
opt h- .byte $43 ; config for v4.3 version .byte c'XAUTORUN ' ; autorun file fname .byte >$0800 ; xB adress for relocator .byte >$0700 ; xB buffer adress for relocator .word $02e2 ; INITAD .word $02e0 ; RUNAD .word $0000 ; custom I/O module - $0000 means use internal xB SIO .word $0000 ; relocator for custom I/O module .byte $ff ; PORTB - you can't swith off BASIC this way .byte $40 ; NMIEN - config at start .byte $c0 ; IRQEN - config at start
Please note that xBIOS do not use page zero. You can change the start address from the third entry above. Now that the above exists, the following examples can be used to access files in the ATR file.
Examples#
Here are some of the examples taken from http://xxl.atari.pl and other online sources, but with a few extra/modified comments in English.
xBIOS_RENAME_ENTRY#
This function allows you to rename a file or directory. There is no limit to the characters used in the filename apart from that they must fit a case insensitive “8.3” format without the dot. If your filename is not 8 characters long, pad it out with spaces.
ldy <fname ldx >fname JSR xBIOS_RENAME_ENTRY fname .byte c'FILENAMESRC '; 11 char ATASCII (8.3 without the dot, space padded) .byte c'FILENAMEDST '; 11 char ATASCII (8.3 without the dot, space padded)
xBIOS_LOAD_FILE#
Load and run the file, INIT and RUN headers are supported. "Boot Loader" has an analogous function xBOOT_LOAD_FILE. In the case of the boot loader if the file does not have a defined block RUN will be launched from the beginning of the first block.
ldy <fname ldx >fname JSR xBIOS_LOAD_FILE fname .byte c'MYFILE COM'; 11 characters ATASCII (8.3 without the dot, space padded)
xBIOS_OPEN_FILE#
Open a file in order to carry out subsequent IO operations.ldy <fname ldx >fname JSR xBIOS_OPEN_FILE fname .byte c'MYFILE COM'; 11 characters ATASCII (8.3 without the dot, space padded)
xBIOS_LOAD_DATA#
Load data from file to a specified address. You can set the file offset (FILE_OFFSET) and the amount of data to be loaded (SET_LENGTH). If you do not define these values, data will be loaded from the current position of the file pointer to the end of the file. If you want to load a binary file using the headers defined in it or use the functions xBIOS_BINARY_LOAD or xBIOS_LOAD_FILE.
ldy <dest ldx >dest JSR xBIOS_LOAD_DATA
xBIOS_WRITE_DATA#
Save data from memory to a file, starting from the current position in the file. You can set the file pointer offset current (FILE_OFFSET) and the amount of data to be saved (SET_LENGTH). If you do not define these values, data from the current file position to the end of the file is written to the file.
ldy <src ldx >src JSR xBIOS_WRITE_DATA
xBIOS_OPEN_CURRENT_DIR#
Opens the current directory.JSR xBIOS_OPEN_CURRENT_DIR
xBIOS_GET_BYTE#
The next byte of an open file is loaded into the register A (accumulator).JSR xBIOS_GET_BYTE
xBIOS_PUT_BYTE#
The byte value in the accumulator is written to a file at it’s current pointer location.
lda BYTE JSR xBIOS_PUT_BYTE
xBIOS_FLUSH_BUFFER#
All write operations are cached, use this to flush the buffer to the current file.
JSR xBIOS_FLUSH_BUFFER
xBIOS_SET_LENGTH#
Defines the amount of data to process while reading or writing. If your OPEN_FILE value is not defined this operation will be carried out until the end of the file.
ldy <len ldx >len JSR xBIOS_SET_LENGTH
xBIOS_SET_INIAD#
Allows you to change the init address vector INITAD ($2E2) for loaded binary files.
ldy <addr ldx >addr JSR xBIOS_SET_INIAD
xBIOS_SET_FILE_OFFSET#
Sets the current read/write position in the current file with a value stored in A, X, Y. This item is calculated relative to the beginning of the file. In DOS speak, the operation is called "POINT".
ldy <pos ldx >pos lda ^pos JSR xBIOS_SET_FILE_OFFSET
xBIOS_SET_RUNAD#
Allows you to change the run address vector RUNAD ($2E0) for loaded binary files.
ldy <addr ldx >addr JSR xBIOS_SET_RUNAD
xBIOS_SET_DEFAULT_DEVICE#
Restores the standard IO device.
JSR xBIOS_SET_DEFAULT_DEVICE
xBIOS_OPEN_DIR#
Allows you to change the current directory.ldy <fname ldx >fname JSR xBIOS_OPEN_DIR
Note that the directory cannot be created by xBIOS and therefore must be created with an external tool such as ‘franny’.
xBIOS_LOAD_BINARY_FILE#
Load and run the binary file from the current read/write position. INIT and RUN headers are supported.
JSR xBIOS_LOAD_BINARY_FILE
xBIOS_OPEN_DEFAULT_DIR#
Opens the default directory.
JSR xBIOS_OPEN_DEFAULT_DIR
xBIOS_SET_DEVICE#
Change the IO device.
ldy <dev ldx >dev JSR xBIOS_SET_DEVICE
xBIOS_RELOCATE_BUFFER#
Change address IO buffer. If before the call to set the marker C = 1, the relocation can be carried out even during IO. The data will not be lost. If the marker before calling C = 0, buffer contents will not be copied to a new location.
ldx >buffer JSR xBIOS_RELOCATE_BUFFER
xBIOS_GET_ENTRY#
Gets another entry in the directory. The X register returns the index to the filename or folder (byte of buffer address is stored in the variable xBUFFERH). The accumulator is set with the status. The carry flag is set when the end of the directory is found.
JSR xBIOS_GET_ENTRY
xBIOS_OPEN_DEFAULT_FILE#
Opens the default file. The function does not search the directory, the file handle is derived from the variable 'Xfile'.
JSR xBIOS_OPEN_DEFAULT_FILE
xBIOS_READ_SECTOR#
Load a sector into a buffer. lda >sector ; High byte of the sector number ldy <sector ; Low byte of the sector number
JSR xBIOS_READ_SECTOR
xBIOS_FIND_ENTRY#
This function allows you to find the specified directory entry. The X register returns the index to the filename or folder (byte of buffer address is stored in the variable xBUFFERH). The accumulator is the status byte. If an entry is not found, the carry flag is set.
ldy <fname ldx >fname JSR xBIOS_FIND_ENTRY
xBIOS_SET_BUFFER_SIZE#
This feature allows you to set the buffer size for IO operations. Buffer Size is also stored in the variable xBUFSIZE in bytes format. lda # $ 100-SIZE
JSR xBIOS_SET_BUFFER_SIZE
Counters During I/O#
xIRQEN equ xBIOS+$3ea ; User IRQ (1 byte)
xSEGMENT equ xBIOS+$3f4 ; Bytes to go in binary file segment (2 bytes)
xNOTE equ xBIOS+$3f6 ; File pointer (3 bytes)
PUPBT1 equ $033D ; Power-up validation byte 1
icl 'atarihw.ah'
opt h+o+l+
org $c00
start_sio sei
lda #$00
sta nmien
sta irqen
sta xIRQEN
sta dmactl
lda #$fe
sta portb
lda <MyNMI
sta nmiv
lda >MyNMI
sta nmiv+1
lda <mydlist
sta dlistl
lda >mydlist
sta dlisth
jsr xBIOS_SET_DEFAULT_DEVICE ; SIO drive
ldx >RESETV
ldy <RESETV
jmp xBIOS_SET_RUNAD ; new runad vector
ini start_sio
org RESETV
.word run_adr ; RUN
org PUPBT1
.byte d'xxl' ; Let the RESET key work as a RESET key
org $0000
run_adr lda #$74
sta colbak
_stop jmp _stop ; Endless loop
mydlist
:12 .byte $70
.byte $46,<counter,>counter
.byte $06
.byte $41,<mydlist,>mydlist
counter .byte d'SEGMENT: '
.byte d'FILE OFFSET: '
start sei
ldx #3
ldy #0
@ inc PORTB
lda $e000,y
_csrc equ *-1
dec PORTB
sta (_csrc-1),y
_cdst equ *-1
dey
bne @-
inc _csrc
dex
bpl @-
@ lda vcount
bne @-
lda #$22
sta dmactl
lda #$40
sta nmien
rts
MyNMI sta nmiA
sty nmiY
inc licz
lda #0
licz equ *-1
lsr @
bcc secondnmi
firstnmi ldy #16
lda xSEGMENT+1
jsr puthex
lda xSEGMENT
jsr puthex
jmp endnmi
secondnmi ldy #20+14
lda xNOTE+2
jsr puthex
lda xNOTE+1
jsr puthex
lda xNOTE
jsr puthex
endnmi lda #0
nmiA equ *-1
ldy #0
nmiY equ *-1
rti
puthex pha
lsr @
lsr @
lsr @
lsr @
jsr nibble
pla
and #$0f
nibble cmp #$0a
sed
adc #$10
cld
sta counter,y
iny
rts
ini start
org $0c00
:$c300 .byte $ff
Playing Music During I/O#
opt h+o+l+
org PUPBT1
.byte d'xxl' ; Let the RESET key work as a RESET key
org $c00
start_sio sei
lda #$00
sta nmien
sta irqen
sta xIRQEN
sta dmactl
lda #$fe
sta portb
lda <MyNMI
sta nmiv
lda >MyNMI
sta nmiv+1
lda #$40
sta nmien
jmp xBIOS_SET_DEFAULT_DEVICE ; SIO drive
MyNMI sta vbisaveA+1
stx vbisaveX+1
speed lda #0
bne wp
loadpat ldx #0
lda pat,x
bmi pass
asl @
asl @
asl @
asl @
sta wp+1
pass inx
lda #$3f
sax loadpat+1
wp ldx #0
lda ins,x
sta audc1
lda frq,x
sta audf1
inc wp+1
dec speed+1
bpl pass2
lda #5
sta speed+1
wp1 lda #$20
sta pass2+1
eor #$60
sta wp1+1
pass2 ldx #0
lda ins,x
sta audc2
inc pass2+1
vbisaveA lda #0
vbisaveX ldx #0
rti
ins .byte $0F,$AF,$AC,$A7,$A2,$00,$04,$A3
.byte $22,$21,$A1,$00,$00,$00,$00,$00
.byte $AF,$AF,$09,$07,$05,$04,$04,$03
.byte $03,$03,$02,$02,$02,$01,$01,$00
.byte $87,$84,$83,$82,$81,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $84,$84,$84,$84,$84,$84,$83,$83
.byte $83,$83,$82,$82,$81,$81,$00,$00
.byte $83,$82,$81,$81,$81,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00
frq .byte $04,$C0,$D0,$E0,$F0,$00,$04,$C0
.byte $D0,$E0,$F0,$00,$00,$00,$00,$00
.byte $98,$A8,$03,$03,$03,$03,$03,$03
.byte $03,$03,$03,$03,$03,$03,$03,$03
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00
.byte $00,$00,$00,$00,$00,$00,$00,$00
pat .byte $00,$80,$00,$80,$01,$80,$00,$00
.byte $80,$00,$00,$80,$01,$80,$03,$80
.byte $00,$80,$00,$80,$01,$80,$02,$02
.byte $00,$80,$01,$01,$80,$00,$03,$80
.byte $00,$80,$00,$80,$01,$80,$00,$00
.byte $80,$00,$00,$80,$01,$80,$03,$80
.byte $00,$00,$00,$80,$01,$00,$00,$80
.byte $00,$80,$01,$01,$80,$00,$01,$00
ini start_sio
org $1000
:$C000 .byte $ff
org $D800
:$2700 .byte $ff
run_adr lda #$74
sta colbak
_stop jmp _stop ; endless loop
run run_adr
Indexed Data within File - LZ4 Graphics Decompression#
xFILE equ xBIOS+$3ec ; File handle
xDAUX3 equ xBIOS+$3f3 ; Buffer offset if AtariDOS FS
xDAUX2 equ xBIOS+$3fd ; Sector hi if AtariDOS FS
xDAUX1 equ xBIOS+$3fe ; Sector lo if AtariDOS FS
PUPBT1 equ $033D ; Power-up validation byte 1
myscr equ $8150
myscr1 equ $9000
colour equ myscr+$1e01
fhandle equ $80
org PUPBT1
.byte d'xxl' ; Let the RESET key work as a RESET key
org $c00
Mydlist .byte $70,$70,$70
.byte $4e,a(myscr)
:93 .byte $0e
.byte $4e,a(myscr1)
:97 .byte $0e
.byte $41,a(Mydlist)
myinit lda #$00
sta DMACTLS
lda <Mydlist
sta DLISTLS
lda >Mydlist
sta DLISTHS
lda #%00100010
sta DMACTLS
load_index ldx load_gfx+1
lda xDAUX1
sta fhandle,x
lda xDAUX2
sta fhandle+1,x
lda xDAUX3
sta fhandle+2,x
cpx #$0c
bne skip
lda #$100-(ldgfx+2-load_gfx)
sta ldgfx+1
bne skip
load_gfx ldx #0
lda fhandle,x
sta xFILE
lda fhandle+1,x
sta xFILE+1
jsr xBIOS_OPEN_DEFAULT_FILE
ldx load_gfx+1
lda fhandle+2,x
sta xDAUX3
skip lda #%1111
sbx #$100-$04
sax load_gfx+1
lda <myscr
sta dest
lda >myscr
sta dest+1
jsr unlz4
ldx #$02
@ lda colour,x
sta COLPF0S,x
dex
bpl @-
ldgfx bmi load_index
unlz4 icl 'unlz4.asm'
ini myinit
opt h-
ins 'DRUID.LZ4',$0b,.FILESIZE 'DRUID.LZ4'-$0b-$06
ins 'LOADING.LZ4',$0b,.FILESIZE 'LOADING.LZ4'-$0b-$06
ins 'SHPOON2.LZ4',$0b,.FILESIZE 'SHPOON2.LZ4'-$0b-$06
ins 'POTATERR.LZ4',$0b,.FILESIZE 'POTATERR.LZ4'-$0b-$06
Use of High Speed Devices#
When you first load xBIOS, you can complete a check to see if your disk drive is ultraspeed (see next example). If so, save a value to xHSPEED. When loading data, copy the value of xHSPEED to xSPEED and use the following code:
lda xHSPEED bmi no_hispeed sta xSPEED
This works in conjunction with: "jsr xBIOS_SET_DEFAULT_DEVICE" If you are using the AtariOS I/O module, speed control is not possible.
Detecting High Speed Devices#
If you want to detect if the user’s disk drive has high speed capabilities, you can detect it’s high speed status using this code.
xBIOS_SET_DEFAULT_DEVICE equ xBIOS+$2A
xBUFSIZE equ xBIOS+$3f1 ; Buffer size lo byte $100-SIZE (1 byte)
xDEVICE equ xBIOS+$3fc ; Device ID
xIOV equ xBIOS+$3ee ; I/O module entry (2 bytes)
xBSIO jmp (xIOV)
start jsr xBIOS_SET_DEFAULT_DEVICE ; I want to use xB SIO I/O
lda #$100-$01 ; set buffer size
sta xBUFSIZE
lda #'1' ; AtariOS device '1' = DOS device D1:
sta xDEVICE ; you can use '2', '3' and so for D2: D3: ...
ldx #$3F ; set command GET HI SPEED FROM DRIVE
jsr xBSIO
bcs DRIVE_HAS_NO_HIGH_SPEED_FUNCTIONS
lda $7ff ; get HiSpeedIndex byte from buffer
; (xBUFSIZE = lo byte,xBUFFERH = hi byte)
Remember to preserve old xBUFSIZE and xDEVICE values if these are required later in your code.
Using Alternative Disk Drives#
If you are using disk drives other than the default D1:, you can save values into xDEVICE in order to refer to the other disk drives.
xDEVICE equ xBIOS+$3fc ; Device ID lda #2 ; Use disk drive number 2 sta xDEVICE
Checking if Alternative Disk Drives Exist#
Apply this code to check if a particular disk drive exists (1-8).
lda #device_number sta xDEVICE jsr status
Varying Directory Sizes#
xBIOS can handle directories of varying sizes as per the directories of different versions of DOS. ‘xDIRSIZE’ (xBIOS+$3e5 in xBIOS 4.3) is used as a read only way to find out the current directory size in sectors. It is one byte in length and is read-only.
A directory entry within Atari DOS 2 / MyDOS and similar DOS’s uses up 16 bytes and looks like this:
.byte status ; Byte 1 .word size ; - in standard directories always $08 ; Bytes 2 and 3 .word first_sector ; Bytes 4 and 5 .byte c'FILENAMEEXT' ; Byte 6 to 16
A standard directory uses 8 sectors (size = $08) which means 8 sectors * 8 entry = 64 max. Top DOS / Bibo DOS with sector sizes of 256 bytes may looks like 8 sectors * 16 entry = 128 maximum. You can make subdirectories of differing sizes eg. size=$02 (16/32 entry) or size = $ff (2040 / 4080 entry). There is no tool to make different size catalogues, if at any time such a tool appears, xBIOS will handle it.
xBOOT#
This isn’t xBIOS as such but a related loader mechanism which is simpler than xBIOS.
Simply download xBOOT from http://xxl.atari.pl and add it to your disk using an external tool such as ‘franny’. Name the first file to load ‘AUTORUN’. This will auto-load.
Within this executable, have the following code to load the next file in a chain.
xBOOT_LOAD_FILE equ $5f1 ldy <fname ldx >fname jmp xBOOT_LOAD_FILE fname .byte c'NEXTPARTCOM' ; 11 chars ATASCII
xBOOT uses 384 bytes at $480 and $f9-$ff in page zero.
Original document from Steve Nicklin (snicklin at AtariAge). Imported into AtariWiki (23/01/2016) to allow peer feedback and improvement.